Surgical suture needles are well known in the medical arts and include primarily two types of needles, taper point type needles and cutting edge type needles. A taper point type surgical needle includes a proximal end portion defining a suture-mounting portion having a hole or channel to which a suture is to be attached, an intermediate portion defining a main body portion having a generally uniform cross-sectional area throughout an entire length thereof, and a distal end portion defining a tapered portion whose cross-sectional area decreases progressively toward a pointed distal end of the suture needle. Cutting edge type needles also taper to a piercing point, however, unlike taper point type needles, cutting edge type needles include one or more cutting edges with an otherwise smooth outer surface.
In the design of either taper point type or cutting edge type surgical needles it is generally desirable for the needles to exhibit favorable strength and ease of penetration characteristics. It is desirable for a surgical needle to be sufficiently strong in order to penetrate tissue which is being sutured without bending or breaking during a surgical procedure. It is also desirable for the surgical needle to easily penetrate and smoothly pass through the tissue being sutured. The amount of force required for the surgical needle to penetrate tissue includes the force required for the engagement of the tip of the needle with the tissue and the subsequent creation of the entry hole as well as the force required for the widening of the entry hole created. The force required for a taper point type surgical needle to widen the hole is greater than the force required for a cutting edge type needle since the taper point type needle merely dilates the hole and does not cut the hole as would a cutting edge type needle.
Taper point type surgical needles typically have a taper from a middle section of the needle body which ends in a distal piercing point. The taper is often expressed as a ratio of the length of the taper section to the diameter of the wire used to form the needle. It is known that the higher the taper ratio is, the more slender the taper, and thus the resistance to penetration and/or piercing through tissue will typically be lessened. However, the more slender the taper, the mechanical strength for needles manufactured from the same material will be lessened. The converse is also to be expected for needles having lower taper ratios.
In practice, the piercing resistance which the suture needle receives from the tissue of the living body is at a maximum level when the surgical needle is first piercing the skin of the tissue. This is due to the fact that the skin of the tissue has a greater rupture strength than the other parts or layers of the tissue. The resistance of the suture needle as the needle pierces through the skin of the tissue greatly depends on the degree of sharpness of the pointed end of the suture needle. Once the suture needle pierces the skin of the tissue, the piercing resistance is abruptly reduced regardless of the value of the cross-sectional area increase rate of the tapered portion.
In view of the above, it is apparent that the design techniques generally employed to meet the above two design criteria of strength and ease of penetration are often in conflict. As stated above, one approach to improve the strength of a needle is to increase the diameter or thickness of the needle. However, by increasing the thickness of the needle, the force necessary to penetrate the tissue is also increased, and the opening left in the tissue after passage of the needle is also enlarged. Similarly, ease of penetration can be improved by making the needle thinner or more slender. However, a reduction in the thickness of the needle will generally result in a corresponding reduction in the strength of the needle. Thus the design of a needle which exhibits favorable strength and penetration characteristics requires that certain tradeoffs be made in the two criteria to arrive at a needle with optimal overall performance.
Accordingly, there is a continuing need for surgical tapered needles exhibiting improved penetrating characteristics (i.e., resistance to penetration through tissue) and improved mechanical characteristics such as bending strength.